Comparing the effectivity of IgG and Fab in immune response modulation

In 1975, Köhler and Milstein described the hybridoma technology for generating monoclonal antibodies (mAb). Some of the advantages of this technique are: (i) Each hybrid cell produces only one antibody which recognizes a specific epitope on the antigen, (ii) As the hybrid cell is immortal, it provides an unlimited supply of antibody, (iii) Purifying of the specific antigen in large quantities could be performed with various methods by using mAb. Microbial infections are frequently diagnosed by detecting specific antigen(s) or antibody(ies) in serum. Enzyme-linked immunosorbent assay ( ELISA ) is one of the diagnostic methods. In different ELISA methods frequently two different mAb are used in order to demonstrate specific antigen(s). However, generating two different mAb is rather difficult as the immune response is usually directed against epitope which is the most immunogenic. However, antibodies which recognize particularly well-presented or immunodominant epitopes are formed especially. In some articles, it was regarded that to generate a different set of antibodies against the antigen, immunogenic epitopes are masked with specific monoclonal antibodies from a first immunization, then the organism can generate a different set of antibodies against the antigen when it meets the antigen / antibody complex a second time. However, passive administration of IgG antibody together with an antigen specifically suppresses the immune response. IgG mediated suppression results from simultaneous interaction of the antigenic portion of the complex with membrane Ig molecules on specific B cells and of the antibody portion of the complex with Fey receptors ( FcyRIIB ) on the same B lymphocytes. The ability of passively administered antibody to suppress the immune response has certain clinical consequences and applications as well. Certain vaccines ( e.g. mumps and measles ) are not generally given to infants before one year of age. This is because levels of maternally- derived IgG remain high for at least six months after birth; the presence of such passively transfered IgG at the time of vaccination would result in the development of an inadequate immune response in baby. In the cases of Rhesus incompatibility the administration of anti-RhD antibody to Rh negative (-) mothers prevents primary sensitization by fetally derived Rh positive (+) blood cells, presumably by removing the foreign antigen ( fetal erytrocytes ) from the maternal circulation. In this study, plasma antibody levels of BALB/c mice immunized either with "antigen+IgG", "antigen+Fab" or "antigen" were compared. Except for PBS group, all groups consisted of S BALB/c mice. When plasma antibody levels were compared, it was observed that antibody response was suppressed in "MFNy+IgG" immunized group. However, antibody levels in "MFNy+Fab'' - immunized group were found to be not significantly suppressed. According to the results obtained from this study using "Ag+Fab" instead of "Ag+IgG" for epitope-masking seemed to be more convenient to generate mAb against different epitopes.